A preliminary animal study of thermal rheology fluid as a new temperature-dependent liquid intravascular embolic material

PURPOSE: Thermal rheology (TR) fluid, which comprises polyethylene (PE) particles, their dispersant, and solvent, is a material that increases in viscosity to various degrees depending on the type and ratio of these constituents when its temperature rises. The viscosity of type 1 (TRF-1) increases more than that of type 2 (TRF-2) near rabbit body temperature. This preliminary animal study aimed to determine the basic characteristics and embolic effect of TR fluid by comparing TRF-1 and TRF-2. MATERIALS AND METHODS: Twenty-four Japanese white rabbits underwent unilateral renal artery embolization using TRF-1 or TRF-2 and follow-up angiography at 7 or 28 days (4 subgroups, n = 6 each). Subsequently, the rabbits were euthanized, and the embolized kidneys were removed for pathological examination. The primary and final embolization rates were defined as the ratio of renal artery area not visible immediately after embolization and follow-up angiography, respectively, to visualized renal artery area before embolization. The final embolization rate and maximum vessel diameter filled with PE particles were compared between materials. Moreover, the embolic effect was determined to be persistent when a two-sided 95% confidence interval (CI) for the difference in means between the embolization rates was < 5%. RESULTS: The final embolization rate was significantly higher for the TRF-1 than for the TRF-2 at both 7 (mean 80.7% [SD 18.7] vs. 28.4% [19.9], p = 0.001) and 28 days (94.0% [3.5] vs. 37.8% [15.5], p < 0.001). The maximum occluded vessel diameter was significantly larger for TRF-1 than for TRF-2 (870 µm [417] vs. 270 µm [163], p < 0.001). The embolic effect of TRF-1 was persistent until 28 days (difference between rates − 3.3 [95% CI − 10.0–3.4]). CONCLUSION: The embolic effect of TRF-1 was more persistent than that of TRF-2, and the persistency depended on the type and ratio of TR fluid constituents.